Serological reactivity of recombinant 1D autoantigen and its expression in human thyroid and eye muscle tissue: A possible autoantigenic link in Graves' patients

Thyroid-associated ophthalmopathy (TAO) is a potentially severe autoimmune disease, in and around the orbit, usually accompanied by Graves' disease. It was the goal of this study to develop a serological indicator for TAO and to characterize its expression in human thyroid and eye muscle tissue. Thus, we have recloned the full-length 1D-complementary DNA and assessed its expression levels in 90 healthy and diseased human thyroids. Only Graves' patients suffering from TAO (n = 29) displayed a significant, 2.1-fold increase of 1D expression levels (P = 0.029), compared with normal controls (n = 9), as assessed using the Mann-Whitney U-test for paired, nonnormally distributed samples. In contrast, a decrease of 1D expression (to 40% of control normal values) was confined to thyroid autonomy (n = 19, P = 0.032). In all other diseased human thyroids, including Graves' thyroids from patients not suffering from clinically overt TAO (n = 9), 1D expression levels were not different from the healthy controls. 1D gene expression was demonstrated in both healthy (n = 10) and diseased (n = 10) eye muscle tissues. Furthermore, a recombinant protein derived from baculovirus-infected Sf9 insect cells was purified under both nondenaturing and denaturing conditions. While under nondenaturing conditions, the molecular mass of recombinant 1D was determined to be 85 kDa; denaturing isolation yielded the expected 64-kDa protein. Autoantibodies against denatured 1D protein were not detectable in sera of diseased or healthy subjects. Immunoreactivity against the 85-kDa, nondenatured protein, evaluated in a panel of 222 different human sera, showed that 82% of Graves' patients suffering from TAO had autoantibodies against recombinant 1D, whereas only 5% of the healthy controls were positive for antibodies against 1D. Taken together, our results demonstrate a high disease sensitivity and specificity of recombinant, nondenatured 1D, to distinguish Graves' disease with or without TAO from other forms of thyroid and/or eye disease. Prospective studies will have to show whether autoantibodies against 1D can also be used as a prognosticator of TAO.